Methods and systems theoretically characterize multiple DC power supply decoupling capacitors in a printed circuit board by analysis of anti-resonant frequencies to help assess compliance with various standards or regulations.
Power distribution is crucial in printed circuit board (PCB) design. DC-to-DC converters are used in printed circuit boards to create a sub-system power source isolated from a main power system. However, an isolated power source is still a power system and must itself suppress noise. Electronic products are subject to various industry standards and regulations regarding electromagnetic radiation and intersystem interference. As electronic data rates have increased into the gigahertz range, the increased signal transition time causes noise along a wide frequency range. Voltage signal noise suppression can be achieved through coupling of the voltage to a power source or ground. The proper design of printed circuit boards used in such products can make the difference between a product passing such signal integrity and electromagnetic compatibility (EMC) standards.
Proper decoupling capacitor design is a key element in a printed circuit board from signal integrity and EMC points of view. Power supply design is evolving and many theories have advanced to address problems. Although the primary focus of power source design is power handling capability, the design of suitable decoupling capacitors is often needed to reduce the radiation and noise emitted from the board. The traditional approach to this problem has been to provide a decoupling capacitance by the strong AC and/or DC coupling of that voltage to a power source or ground. This has been achieved by providing the printed circuit board with the addition of numerous discrete decoupling capacitors. However, analyzing suitable decoupling capacitors becomes difficult, particularly when printed circuit boards have multiple DC power supplies on the board and a large number of discrete capacitive components.
Conventional methods have relied on a trial-and-error physical testing of assembled boards to assess compliance with various regulations and standards. If the boards do not meet standards, various decoupling capacitor arrangements were modified and retested. This actual testing for compliance through trial and error design and testing has been both time-consuming and costly. It also requires test equipment to perform the testing. Often, this sophisticated testing in a controlled environment required sending of a designed printed circuit board (PCB) to a suitable test facility for testing. This is inconvenient and lengthens the design phase of a project waiting for compliance assurances.